Exploring new tools to add to my toolbox

Luggable Frame Experiment #1

The dimensions for my Luggable PC project were determined by the components within. The width and height, specifically, were dictated by the LCD screen module. Even though I made the CAD files public for anybody to build their own Luggable PC, in practical terms only people with the exact same LCD module would be able to use the files without modification.

A friend who saw the Luggable PC was interested in generalizing the concept and create a frame for lugging a (not disassembled) screen alongside its (also not disassembled) PC. Relative to my project, it would be easier to build and less specialized to the components within, with a trade-off in larger size and heavier weight.

I thought it was a great idea to explore and joined in the experiment. We each came up with a design, and we built both of them at Tux-Lab to see how the ideas translated into reality.

This blog post is a brief summary of my first experiment.

The Components

The monitor is an Yamakasi Catleap monitor, built around a 27″ IPS panel with 2560×1440 resolution. The specific dimensions don’t really matter, as it will be mounted via the standard 75mm VESA pattern on the back. Any large monitor with 75mm VESA pattern would fit as-is, and only minor modifications would be necessary to accommodate monitors with a different mounting pattern.

The PC is a HP Z220, small form factor PC from the HP business line available with a range of components to trade off processing power against price. For the purposes of this experiment, the important details are its height of 331mm and depth of 100mm. Thought not a standardized dimension, many small form factor PCs are roughly the same size.

The Construction

The core of the frame are built from 15mm aluminum extrusions (Misumi HFS3) for strength and the remainder of the frame are made from 6mm laser-cut acrylic fastened to the extrusions via M3 nuts and bolts.

Making the panels from laser-cut acrylic has the advantage of simpler modifications. Many of the critical dimensions in my Luggable PC 3D CAD file has the problem that, when changed, they trigger cascading changes that need to be reconciled. When designing for the 2D tool path of laser laser cutting, it is easier to keep modifications in mind so that a change in one sheet does not cascade to other sheets.

Example #1: The frame has a 331mm x 100mm hole to fit the Z200 case. This can be adjusted to fit any other SFF frame without cascading changes to other components.

Example #2: The monitor mount pattern can be changed, and the mount position can be moved up or down to adjust elevation of the monitor.

The Result

I had never designed for laser cutting before and was happy for the chance to do something on the Tux-Lab laser cutter. I knew that, having little experience with the material, my first few designs will have some amateurish flaws. So this frame #1 was fairly minimalist just to see what happens.

I didn’t have a good grasp how many fasteners I would need to hold everything together. I laser-cut roughly double the number of fastener positions than what I think I would need, as it is easier to have more options rather than less. For the assembly I only installed fasteners in every other hole.

The screen mount was surprisingly successful. We questioned whether 6mm acrylic would be suitable for holding up the Catleap monitor by its 75mm VESA mounts. When we found some worrisome flex, the suspicion went immediately to the 6mm acrylic but it turned out the Catleap monitor enclosure was the source of the flex.

When attempting to install the PC, we found that the case itself would fit just fine but the rubber feet attached to the side of the case did not. I added cutouts in the CAD file but it seemed wasteful to cut entirely new pieces of acrylic just for the little feet cutouts. For purposes of experimentation, a Dremel tool was used to cut gaps to clear the rubber feet.

After the frame was assembled with the screen and the PC, we started plugging in all the cables and wires and I realized I had forgotten to account for the cables. There’s no good place to coil up the excess so they kind of dangle and stand ready to catch on something inconvenient.

The entire assembly was built in a tiny fraction of the time of my Luggable PC and included a much larger monitor with a much higher resolution. The trade off was almost doubling of the weight. The handle, part of the acrylic assembly, appeared to be sufficient to manage the weight.

I carried it across Tux-Lab and quickly encountered the first failure.

The Failure

Lesson of the Day: Sharp internal corners are bad.

My amateur mistake was cutting a sharply cornered rectangle to hold the PC. The sharp corners concentrated the physical load of the PC into a small point in the 6mm acrylic, which protested the poor design by breaking apart.